Friendly reminder: In Half-Blood Prince, while he was invisible in the Slytherin compartment, Harry watched Draco change into his school robes.

QUOTE:“I can see Hogwarts,” said Malfoy, clearly relishing the effect he had created as he pointed out of the blackened window. “We’d better get our robes on.”Harry was so busy staring at Malfoy, he did not notice Goyle reaching up for his trunk;

I’m pretty sure harry fucking potter would be dead obvious when he has decided that he wants to marry Draco. He’ll say something like “just out of pure curiosity what’s your ring size?” and Draco would spit his drink.